JP2000253271A - Waveform generation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To generate a correction waveform which can correspond to CRT of a flat screen by giving the dynamic voltage of a constant period as a prescribed reference voltage. SOLUTION: Not constant voltage but dynamic parabolic waveform voltage is amplitude-adjusted and is inputted in an amplitude adjusting circuit 18 as an H bias. When the amplitude of the output voltage of an operational amplifier 17 becomes larger than the H bias of a parabolic waveform, discharge current is made small. When it is small, feedback control is executed so that discharge current becomes large. In an AGC circuit 21, the discharge current of a capacitor 16 is controlled with the parabolic waveform voltage of an H period as reference voltage and the amplitude of parabolic waveform voltage is changed in the amplitude adjusting circuit 18. Thus, the output waveform of the operational amplifier 17 is changed into a bathtub waveform and it is used as the correction waveform of the focus correction circuit of CRT. Thus, a uniform focus characteristics can be obtained in a whole screen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform generation circuit for generating a horizontal period waveform and setting the amplitude of the waveform based on a predetermined reference voltage.
The present invention relates to a waveform generation circuit suitable for use in generating a correction waveform of a focus correction circuit of a cathode ray tube (CRT) or a convergence correction circuit.

[0002]

2. Description of the Related Art FIG. 10 shows a sectional structure of a CRT. In the figure, an electron beam emitted from an electron gun 101 built in a CRT scans a surface of a panel 103 by being bent in a trajectory by a deflection yoke 102 arranged in a neck portion of the CRT. At this time, the deflection yoke 10
The position at which the electron beam begins to be affected by 2 is called a deflection center. The distance from the deflection center to the panel 103 is longer at the periphery than at the center of the screen.

Here, the electron beam is focused on the panel surface by the medium pressure applied to the electrode of the electron gun 101, but as described above, the distance from the center of deflection to the panel 103 varies depending on the screen position. It is necessary to dynamically change the medium pressure applied to the electron gun 101. This voltage is called a dynamic focus voltage. Normally, as shown in the waveform diagram of FIG. 11, a waveform voltage obtained by amplifying a horizontal period and a vertical period of a parabolic wave is used as the dynamic focus voltage, and the amplified voltage is added to the medium pressure to be applied to the electron gun 1.
01 is applied to the electrode.

FIG. 12 shows an example of a typical parabolic waveform generation circuit. In FIG. 12, the H trigger pulse is differentiated by a differentiating circuit 111, so that its rising timing is converted into a narrow pulse and applied to the set input of the flip-flop 112 as a set pulse.
The flip-flop 112 is set in response to the set pulse, and the switch 113 is turned on (closed) by the set output.

One end of the switch 113 is connected to one end of a capacitor 114 and an inverting (-) input terminal of an operational amplifier 115, and the other end of the switch 113 is connected to a negative power supply VEE.
Is connected to a constant current source 115. And
When the switch 113 is turned on, the constant current source 116
This causes the capacitor 114 to be charged. This results in a retrace of the sawtooth wave. Note that the operational amplifier 115
The non-inverting (+) input terminal is grounded, and the output terminal is connected to the other end of the capacitor 114, and forms an integration circuit with the capacitor 114.

On the other hand, a DC voltage Vdc which is an H bias
Is supplied to a constant current source 116 as a control input for controlling the current (charging current), and the comparator 11
7 inverting input. This comparator 11
The output waveform of the operational amplifier 115 is given to the non-inverting input terminal of the switch 7. Then, when the peak of the sawtooth wave, which is the output waveform of the operational amplifier 115, exceeds the DC voltage Vdc, the output of the comparator 117 is inverted, and this is supplied to the flip-flop 112 as a reset pulse.

The flip-flop 112 enters a reset state in response to the reset pulse, and the reset output turns off (opens) the switch 113. A constant current source 118 is connected between one end of the switch 113 and the positive power supply VDD. When the switch 113 is turned off, the electric charge of the capacitor 114 is discharged by the constant current source 118. This discharge occurs at the next H
It continues until a trigger is input.

The output waveform of the operational amplifier 115 is inverted by an inverting amplifier 122 including resistors 119 and 120 and an operational amplifier 121, and the AGC (automatic gain control) is performed.
rol) circuit 123. This AGC circuit 123
Uses the output waveform of the operational amplifier 115 as a control input, and controls the current (discharge current) of the constant current source 118 by the output. That is, when the amplitude of the output waveform is larger than the DC voltage Vdc, the feedback control is performed such that the discharge current is reduced, and when the amplitude is smaller, the discharge current is increased.

Thus, in the AGC circuit 123,
By performing feedback control of the discharge current of the capacitor 114 using a constant voltage (DC voltage Vdc) as a reference voltage, an output waveform having a constant amplitude can be obtained. Capacitor 114
Has a current value proportional to the H bias, the retrace time is substantially constant even if the amplitude is changed by the H bias. This operational amplifier 11
5 is H.5. Saw +, and is further inverted by the inverting amplifier 122 to be H.Saw +. Saw−.

The output waveform (sawtooth wave) of the operational amplifier 115 and the waveform inverted by the inverting amplifier 122 are multiplied by a multiplier 124 to form a parabolic waveform. And this parabolic waveform is H. Para-, which is further inverted by an inverting amplifier 128 including resistors 125 and 126 and an operational amplifier 127, and Pa
derived as ra +.

The amplitude of the sawtooth wave and the parabolic wave generated in this manner is controlled by the H-biased DC voltage Vdc. That is, by changing the voltage value of the DC voltage Vdc, it is possible to change the amplitude of the sawtooth wave and the parabola wave. Then, by amplifying the parabolic wave to a specified voltage and supplying it to the focus electrode of the CRT, uniform focus characteristics can be obtained over the entire screen.

[0012]

However, in recent years, CR
As for T, in addition to increasing the resolution, flattening with an increased curvature of the panel (tube surface) is progressing, and the demand for focus is also increasing. However, as shown in FIG. 13A, in a conventional CRT having a small curvature of the tube surface, a uniform focus characteristic can be obtained over the entire screen by using the parabolic wave generated as described above. But Figure 1
As shown in FIG. 3 (B), a flat screen CRT has a small voltage change at the center of the screen and a large voltage change at the periphery, so that it cannot be handled by a simple parabolic wave.

At present, demands for convergence deviation (misconvergence) are becoming more severe. The convergence can be corrected by a method of correcting the winding distribution of the deflection yoke and a correction circuit mounted on the deflection yoke, or a method of correcting the convergence by flowing a current from the correction circuit to the correction coil. In the former correction method, it is necessary to additionally correct the remaining correction by a magnetic material such as permalloy. In addition, the correction may cause image distortion and focus deterioration.

Therefore, as in the latter correction method, it is desirable in terms of characteristics to correct the current by flowing an appropriate current through the correction coil. However, as a correction current to be passed through the correction coil, a correction current having a horizontal cycle and a amplitude-modulated horizontal cycle correction current are required in addition to a correction waveform having a vertical cycle.

The present invention has been made in view of the above-mentioned problems, and has as its object to provide a flat screen C
It is an object of the present invention to provide a waveform generation circuit that can generate a correction waveform that can support RT.

[0016]

SUMMARY OF THE INVENTION A waveform generating circuit according to the present invention generates a waveform having a horizontal period and, when the amplitude of the waveform is set based on a predetermined reference voltage, has a constant period as the reference voltage. The configuration is such that a dynamic voltage is applied.

In the waveform generating circuit having the above configuration, for example, a dynamic voltage having a horizontal cycle is applied as a predetermined reference voltage, thereby changing the shape of an output waveform having a horizontal cycle. Further, by applying a dynamic voltage having a vertical cycle, for example, as a predetermined reference voltage, the amplitude of an output waveform having a horizontal cycle is modulated with a vertical cycle.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing a configuration example of a waveform generating circuit according to the first embodiment of the present invention. In FIG.
First, a pulse having a horizontal period is given as an H trigger (hereinafter, referred to as an H trigger pulse). This H trigger pulse is differentiated by the differentiating circuit 11. Thereby, a thin pulse is output from the differentiating circuit 11 at the rising timing of the H trigger pulse. This thin pulse is given to the flip-flop 12 as its set pulse.

The flip-flop 12 enters a set state in response to the set pulse, and provides its set output to the switch 13 as its switching pulse. A constant current source 14 is connected between one end of the switch 13 and the positive power supply VDD, and a constant current source 15 is connected between the other end of the switch 13 and the negative power supply VEE. One end of the switch 13 is connected to one end of the capacitor 16 and the inverting input end of the operational amplifier 17. The operational amplifier 17 has a non-inverting input terminal grounded and an output terminal connected to the other end of the capacitor 16 to form an integration circuit together with the capacitor 16.

On the other hand, a dynamic voltage having a horizontal period, for example, a parabola waveform voltage is amplitude-adjusted by an amplitude adjusting circuit 18 and then applied as an H bias via a voltage follower 19. The H bias is supplied to the constant current source 15 as a control input for controlling the current (discharge current), and also to the inverting input terminal of the comparator 20. The output waveform of the operational amplifier 17 is given to the non-inverting input terminal of the comparator 20. Comparator 1
The comparison output pulse 7 is given to the flip-flop 12 as its reset pulse.

The output waveform of the operational amplifier 17 is a sawtooth wave. Saw +, and is given to the AGC circuit 21 as its control input.
Inverting amplifier 25 composed of 2, 23 and operational amplifier 24
Is inverted at H. Saw-
It is supplied to the AGC circuit 21. This AGC circuit 21
The current (discharge current) of the constant current source 14 is controlled by the output.

The output waveform of the operational amplifier 17 and the waveform inverted by the inverting amplifier 25 are multiplied by a multiplier 26, so that the multiplier 26 has a middle portion having a gentler curve than the parabolic waveform. A waveform (hereinafter, referred to as a bathtub waveform) is output. This bathtub waveform is based on H.264. Derived as a bathtub,
28 and an operational amplifier 29. Derived as bathtub +.

Next, the circuit operation of the waveform generating circuit according to the first embodiment having the above configuration will be described.

First, a pulse having a horizontal cycle is input as an H trigger pulse, and this H trigger pulse is supplied to a differentiating circuit 1.
By being differentiated by 1, the rising timing is converted into a narrow pulse, which is given to the flip-flop 12 as the set pulse. Flip-flop 12
Is set in response to the set pulse, and the switch 13 is turned on by the set output. Then, the capacitor 16 is charged by the charging current flowing through the constant current source 15. This results in a retrace of the sawtooth wave.

On the other hand, instead of a constant voltage, a dynamic voltage, for example, a horizontal period parabolic waveform voltage is adjusted as a predetermined amplitude by the amplitude adjusting circuit 18 as the H bias and input. This parabolic waveform voltage controls the current of the constant current source 15, that is, the charging current of the capacitor 16. Also,
In the comparator 20, the output voltage of the operational amplifier 17 is compared with the parabolic waveform voltage, and the comparison output is given to the flip-flop 12 as its reset pulse.

The flip-flop 12 enters a reset state in response to the reset pulse, and the switch 13 is turned off by the reset output. Then, the charge of the capacitor 16 is discharged through the constant current source 14. The current of the constant current source 14, that is, the discharge current, is controlled by the AGC circuit 21. That is, when the amplitude of the output voltage of the operational amplifier 17 is larger than the H bias of the parabolic waveform, the feedback control is performed such that the discharge current is reduced, and when the amplitude is smaller, the discharge current is increased.

As described above, in the AGC circuit 21, H
Capacitor 1 with periodic parabolic waveform voltage as reference voltage
By controlling the discharge current of No. 6 and changing the amplitude of the parabolic waveform voltage by the amplitude adjusting circuit 18, the output waveform of the operational amplifier 17 changes as shown in the waveform diagram of FIG. That is, in FIG. 2, when the H bias is a constant voltage, the waveform becomes a sawtooth waveform shown by a solid line, whereas by giving a parabolic waveform having an H cycle as the H bias, a substantially inverted S-shaped waveform is obtained, and By changing the amplitude of the parabola waveform, the amplitude of the substantially inverted S-shaped waveform also changes.

The output waveform of the operational amplifier 17 is H.264. Saw
+, Which is further inverted by the inverting amplifier 25 and Saw−. Further, by multiplying the output waveform of the operational amplifier 17 and a waveform obtained by inverting the output waveform by the inverting amplifier 25 by the multiplier 26, as shown in the waveform diagram of FIG. A gentle bathtub waveform is obtained. Then, by changing the amplitude of the parabolic waveform given as the H bias, the degree of swelling of the middle portion of the bathtub waveform changes as shown in the waveform diagram of FIG. This bathtub waveform is shown in FIG. Derived as a bathtub, and an inverting amplifier 3
H. Derived as bathtub +.

The bathtub waveform thus generated,
That is, as shown in FIG. 13B, a flat screen CRT is used as a correction waveform of the focus correction circuit of the CRT by using a waveform whose middle portion is gentler than the parabolic waveform as a correction waveform. In particular, uniform focus characteristics can be obtained over the entire screen in the horizontal scanning direction.

FIG. 5 is a circuit diagram showing a configuration example of a waveform generation circuit according to the second embodiment of the present invention. In FIG.
A pulse having a horizontal period is input as an H trigger pulse. This H trigger pulse is differentiated by the differentiating circuit 31. As a result, a thin pulse is output from the differentiating circuit 31 at the rising timing of the H trigger pulse. This thin pulse is given to the flip-flop 32 as its set pulse.

The flip-flop 32 enters a set state in response to the set pulse, and supplies its set output to the switch 33 as its switching pulse. A constant current source 34 is connected between one end of the switch 33 and the positive power supply VDD, and a constant current source 35 is connected between the other end of the switch 33 and the negative power supply VEE. One end of the switch 33 is connected to one end of the capacitor 36 and the inverting input end of the operational amplifier 37. The operational amplifier 37 has a non-inverting input terminal grounded and an output terminal connected to the other end of the capacitor 36, thereby forming an integrating circuit together with the capacitor 36.

On the other hand, a dynamic voltage of a vertical cycle, for example, a parabolic waveform voltage is amplitude-adjusted by an amplitude adjusting circuit 38, and then applied as a V bias via a voltage follower 39. This V bias is supplied to the constant current source 35 as a control input for controlling the current (discharge current), and also to the inverting input terminal of the comparator 40. The output waveform of the operational amplifier 37 is given to a non-inverting input terminal of the comparator 40. Comparator 3
The comparison output pulse No. 7 is supplied to the flip-flop 32 as its reset pulse.

The output waveform of the operational amplifier 37 is a sawtooth wave. Saw +, and is given to the AGC circuit 41 as its control input.
Inverting amplifier 45 composed of 2, 43 and operational amplifier 44
Is inverted at H. Saw-
It is supplied to the AGC circuit 41. This AGC circuit 41
The current (discharge current) of the constant current source 34 is controlled by the output.

The output waveform of the operational amplifier 37 and the waveform inverted by the inverting amplifier 45 are multiplied by a multiplier 46, whereby a parabolic waveform having a horizontal period and an amplitude modulated at a vertical period is output from the multiplier 46. Is done. This parabolic waveform is described in H. Para-, which is further inverted by an inverting amplifier 50 including resistors 47 and 48 and an operational amplifier 49, and Derived as Para +.

As described above, by applying a parabolic waveform voltage having a vertical cycle instead of a constant voltage as a bias for controlling the amplitude of the output waveform, as shown in the waveform diagram of FIG. A horizontal period parabola waveform whose amplitude is modulated is obtained. By using the parabolic waveform generated in this manner as a correction waveform of the focus correction circuit of the CRT, even in the case of a CRT having a flat screen, a uniform focus characteristic is obtained over the entire screen, particularly in the vertical scanning direction. Can be obtained.

As a bias (reference voltage) for controlling the amplitude of the output waveform, a parabolic waveform having a horizontal cycle is given in the first embodiment, and a parabolic waveform having a vertical cycle is given in the second embodiment. As shown in the figure, the two dynamic waveforms are added by an adder 51,
It is also possible to control the amplitude of the added waveform by the amplitude adjustment circuit 52 and to apply it as a bias. According to this modification, a CRT having a tube surface of any shape
Can be obtained, and a uniform focus can be obtained over the entire screen.

In each of the above-described embodiments, the generated correction waveform is used for focus correction of a CRT having a flat display surface to obtain uniform focus over the entire screen. However, the present invention is not limited to a CRT having a flat display surface. , Wide screen C
The same can be applied to RT focus correction.

As described above, according to the waveform generation circuit of the present invention, it is easy to control the output waveform according to the amplitude and type of the input waveform,
Changing the waveform shape and amplitude modulation can be realized simultaneously by one circuit. In addition, since it is easy to arbitrarily change the waveform at each point, it is possible to obtain optimal image quality over the entire screen. Furthermore, since it is sufficient to provide a waveform of a fixed cycle from the outside and simply add a new circuit for adjusting the amplitude, the conventional waveform generation in which the amplitude of the output waveform is controlled by an external DC voltage. It is also applicable to ICs.

By the way, as in the case of the focus, R (red) G (green) B
There is convergence so that the (blue) beam spot shines at the same position on the CRT tube surface. When a correction current is passed from the correction circuit to the correction coil for correcting the deviation of the convergence, the correction waveform is given to the correction circuit according to the above-described first and second embodiments or modifications thereof. The waveform generated by such a waveform generation circuit becomes valid.

FIG. 8 shows how the RGB beam spots are shifted when the convergence is not corrected. In the state where the misconvergence occurs, the misconvergence can be corrected as shown in FIG. 9 by flowing a correction current of a parabolic waveform having a constant amplitude in a horizontal cycle through the convergence correction coil.

However, this can be said in the case of a CRT having a small curvature of the tube surface as shown in FIG. 13A, and as shown in FIG.
In the case of T, if misconvergence is corrected with a parabolic waveform having a constant amplitude in the horizontal cycle, a convergence shift may occur in the middle part. In such a case, the bathtub waveform obtained by giving the horizontal period parabolic waveform as the H bias becomes effective.

In particular, as shown in FIG. 9, a parabolic waveform obtained by amplitude-modulating a horizontal cycle parabolic waveform in a vertical cycle is effective for correcting a convergence shift occurring at a corner of a screen. In other words, by performing convergence correction using a waveform obtained by modulating the amplitude of a horizontal period parabola waveform with a vertical period, misconvergence occurring at a corner portion of the screen can be reliably corrected.

[0044]

As described above, according to the present invention,
In a waveform generation circuit that generates a horizontal cycle waveform and sets the amplitude of the waveform based on a predetermined reference voltage, a dynamic voltage having a fixed cycle is provided as the reference voltage instead of a fixed voltage. By
Since the shape of the output waveform can be changed or its amplitude can be modulated, it is possible to easily generate a correction waveform compatible with a flat screen CRT.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration example of a waveform generation circuit according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an H.264 according to the first embodiment. FIG. 7 is a waveform diagram showing a waveform change of Saw ± waveform.

FIG. 3 is a waveform diagram showing a parabola waveform and a bathtub waveform.

FIG. 4 is a diagram illustrating an H.264 according to the first embodiment. FIG. 6 is a waveform chart showing a change in waveform of a bathtub ± waveform.

FIG. 5 is a circuit diagram illustrating a configuration example of a waveform generation circuit according to a second embodiment of the present invention.

FIG. 6 is a waveform diagram showing an output waveform obtained by modulating a horizontal period parabola waveform with a vertical period.

FIG. 7 is a block diagram illustrating a configuration in which a horizontal period parabola waveform and a vertical period parabola waveform are added and applied as a bias;

FIG. 8 is a diagram showing a state before convergence correction.

FIG. 9 is a diagram showing a state after convergence correction.

FIG. 10 is a sectional structural view of a CRT.

FIG. 11 is a waveform diagram showing a conventional dynamic focus waveform.

FIG. 12 is a circuit diagram showing a conventional example of a waveform generation circuit.

FIG. 13 is a diagram showing a conventional CRT (A) having a small curvature of a tube surface and a CRT (B) having a flat screen.

[Explanation of symbols]

11, 31 ... differentiation circuit, 14, 15, 34, 35 ... constant current source, 16, 36 ... capacitor, 18, 38 ... amplitude adjustment circuit, 20, 40 ... comparator, 21, 41 ... AGC
Circuit, 25, 30, 45, 50 ... inverting amplifier

Claims (7)

[Claims] 1. A waveform generation circuit for generating a horizontal period waveform and setting the amplitude of the waveform based on a predetermined reference voltage, wherein a predetermined period dynamic voltage is provided as the predetermined reference voltage. A waveform generation circuit characterized in that: 2. The waveform generating circuit according to claim 1, further comprising means for controlling an amplitude of said dynamic voltage. 3. A dynamic voltage having a horizontal period is provided as the predetermined reference voltage.
The described waveform generation circuit. 4. The method according to claim 1, wherein a vertical period dynamic voltage is applied as the predetermined reference voltage.
The described waveform generation circuit. 5. The waveform generating circuit according to claim 1, wherein a dynamic voltage having a horizontal period and a dynamic voltage having a vertical period are added and given as the predetermined reference voltage. 6. The waveform generation circuit according to claim 1, wherein a correction waveform used for a focus correction circuit of a CRT is generated. 7. The waveform generation circuit according to claim 1, wherein a correction waveform used for a convergence correction circuit of a CRT is generated.